Light-emitting diode module having light-emitting diode joined through solder paste and light-emitting diode

ABSTRACT

Disclosed are a light emitting diode and a light emitting diode module. The light emitting diode module includes a printed circuit board and a light emitting diode joined thereto through a solder paste. The light emitting diode includes a first electrode pad electrically connected to a first conductive type semiconductor layer and a second electrode pad connected to a second conductive type semiconductor layer, wherein each of the first electrode pad and the second electrode pad includes at least five pairs of Ti/Ni layers or at least five pairs of Ti/Cr layers and the uppermost layer of Au. Thus a metal element such as Sn in the solder paste is prevented from diffusion so as to provide a reliable light emitting diode module.

CROSS REFERENCE TO RELATED APPLICATION

This patent document is a continuation of U.S. patent application Ser.No. 14/848,250 filed Sep. 8, 2015, which is a continuation of and,claims the benefits of and priority to, a Patent Cooperation Treaty(PCT) Application No. PCT/KR2014/003705, filed on Apr. 28, 2014, whichfurther claims priorities from and the benefits of Korean PatentApplication No. 10-2013-0049053, filed on May 1, 2013, Korean PatentApplication No. 10-2013-0101736, filed on Aug. 27, 2013, and KoreanPatent Application No. 10-2013-0151438, filed on Dec. 6, 2013, which areall hereby incorporated by reference for all purposes as if fully setforth herein.

TECHNICAL FIELD

This patent document relates to a light emitting diode and a lightemitting diode module. Some embodiments of this patent document relateto a light emitting diode module including a light emitting diode bondedto a substrate such as a printed circuit board and the like via a solderpaste.

BACKGROUND

Since development of gallium nitride (GaN)-based light emitting diodes(LEDs), the GaN-based LEDs are used in various application rangesincluding natural color LED display devices, LED traffic signboards,white LEDs, and the like.

Generally, a GaN-based LED is formed by growing epitaxial layers on asubstrate such as a sapphire substrate, and includes an N-typesemiconductor layer, a P-type semiconductor layer and an active layerinterposed therebetween. An N-electrode pad is formed on the N-typesemiconductor layer and a P-electrode pad is formed on the P-typesemiconductor layer. The light emitting diode is electrically connectedto an external power source through the electrode pads. In operation,current flows from the P-electrode pad to the N-electrode pad throughthe semiconductor layers.

SUMMARY

Embodiments of the disclosed technology provide an LED module thatincludes a light emitting diode bonded to a substrate via solder paste.

Embodiments of the disclosed technology a light emitting diode capableof preventing diffusion of metal elements of solder paste, and an LEDmodule including the same.

Embodiments of the disclosed technology a light emitting diode havingimproved current spreading performance.

Embodiments of the disclosed technology provide a light emitting diodecapable of improving light extraction efficiency through improvement ofreflectivity.

Embodiments of the disclosed technology provide a light emitting diodeenabling simplification of a fabrication process while improving currentspreading performance, an LED module including the same, and a method offabricating the same.

In one aspect, a light emitting diode module is provided to include aprinted circuit board; and the light emitting diode bonded to theprinted circuit board. The light emitting diode may comprise a firstconductive-type semiconductor layer; a plurality of mesas placed on thefirst conductive-type semiconductor layer and each including an activelayer and a second conductive-type semiconductor layer; a firstelectrode pad electrically connected to the first conductive-typesemiconductor layer; and a second electrode pad electrically connectedto the second conductive-type semiconductor layer of each of the mesas,wherein the first electrode pad and the second electrode pad arerespectively bonded to corresponding pads on the printed circuit boardvia solder paste, and each of the first electrode pad and the secondelectrode pad comprises a solder barrier layer and an oxidation barrierlayer.

Since each of the first and second electrode pads includes the solderbarrier layer, it is possible to prevent metal elements such as Sn inthe solder paste from diffusing into the light emitting diode.

In some implementations, the light emitting diode may further includereflective electrode structures respectively placed on the mesas; and acurrent spreading layer covering the plurality of mesas and the firstconductive-type semiconductor layer, including openings respectivelyplaced in upper regions of the mesas while exposing the reflectiveelectrode structures, wherein the current spreading layer forms ohmiccontact with the first conductive-type semiconductor layer and isinsulated from the plurality of mesas, wherein the first electrode padis electrically connected to the current spreading layer and the secondelectrode pad is electrically connected to the reflective electrodestructures.

Since the current spreading layer covers the plurality of mesas and thefirst conductive-type semiconductor layer, the light emitting diode hasimproved current spreading performance.

In some implementations, each of the reflective electrode structures mayinclude a reflective metal section; a capping metal section; and anoxidation prevention metal section, the reflective metal section havingan inclined side surface such that an upper surface of the reflectivemetal section has a narrower area than a lower surface thereof, thecapping metal section covering the upper and side surfaces of thereflective metal section. Further, the oxidation prevention metalsection covers the capping metal section, a stress relief layer beingformed at an interface between the reflective metal section and thecapping metal section. The stress relief layer relieves stress due to adifference in coefficient of thermal expansion between different metallayers.

In some implementations, the plurality of mesas may have an elongatedshape extending in one direction and may be parallel to each other, andthe openings of the current spreading layer may be placed to be biasedtowards the same ends of the plurality of mesas.

In some implementations, the current spreading layer includes areflective metal. In some implementations, the current spreading layermay have a reflectivity of 65% to 75%. With this structure, it ispossible to provide light reflection by the current spreading layer inaddition to light reflection by the reflective electrodes, whereby lighttraveling through sidewalls of the plurality of mesas and the firstconductive-type semiconductor layer can be reflected.

In some implementations, the light emitting diode may further include anupper insulation layer covering at least part of the current spreadinglayer and including openings exposing the reflective electrodestructures, wherein the second electrode pad is placed on the upperinsulation layer and electrically connected to the reflective electrodestructures exposed through the openings of the upper insulation layer.

In some implementations, the light emitting diode may further include ananti-diffusion reinforcing layer placed between the reflective electrodestructures and the second electrode pad. In some implementations, theanti-diffusion reinforcing layer can prevent metal elements diffusingthrough the second electrode pad from entering the light emitting diode.In some implementations, the anti-diffusion reinforcing layer may beformed of the same material as that of the current spreading layer.

In some implementations, the light emitting diode may further include alower insulation layer placed between the plurality of mesas and thecurrent spreading layer and insulating the current spreading layer fromthe plurality of mesas, the lower insulation layer including openingsrespectively placed in the upper regions of the mesas and exposing thereflective electrode structures.

In some implementations, the openings of the current spreading layer mayhave a greater width than the openings of the lower insulation layer soas to allow all of the openings of the lower insulation layer to beexposed therethrough.

In some implementations, the light emitting diode may further include anupper insulation layer covering at least part of the current spreadinglayer and including openings exposing the reflective electrodestructures, wherein the upper insulation layer may cover sidewalls ofthe openings of the current spreading layer.

In some implementations, the lower insulation layer may include asilicon oxide layer and the upper insulation layer may include a siliconnitride layer. In some implementations, the upper insulation layerformed of the silicon nitride layer can prevent metal elements of thesolder paste from diffusing therethrough.

In some implementations, the light emitting diode may further include asubstrate and a wavelength converter covering a lower surface of thesubstrate. In some implementations, the substrate may be a growthsubstrate for growing semiconductor layers. Furthermore, the wavelengthconverter may cover the lower surface and a side surface of thesubstrate.

In some implementations, the solder barrier layer may include a metallayer including Cr, Ti, Ni, Mo, TiW or W, or a combination of any two ofCr, Ti, Ni, Mo, TiW or W, and the oxidation barrier layer includes anAu, Ag or organic material layer.

In some implementations, the solder paste may cover at least part of aside surface of each of the first electrode pad and the second electrodepad.

In some implementations, the solder paste may contact a lower surface ofthe light emitting diode adjacent to the first electrode pad and thesecond electrode pad. In some implementations, the light emitting diodemay further include an upper insulation layer placed on the lowersurface thereof, and the solder paste may contact the upper insulationlayer. In some implementations, the solder paste may partially cover aside surface of the light emitting diode.

In some implementations, the solder paste may contain Sn and othermetals, and Sn may be present in an amount of 50 wt % or more based onthe total weight of the solder paste. In some implementations, Sn may bepresent in an amount of 60 wt % or more, for example, 90 wt % or more,based on the total weight of the solder paste.

In some implementations, the light emitting diode further comprises:reflective electrode structures placed over the mesas; and a currentspreading layer covering the plurality of mesas and the firstconductive-type semiconductor layer, wherein the current spreading layeris disposed to form openings exposing at least a portion of thereflective electrode structures and the current spreading layer formsohmic contact with the first conductive-type semiconductor layer and isinsulated from the plurality of mesas, wherein the first electrode padis electrically connected to the current spreading layer and the secondelectrode pad is electrically connected to the reflective electrodestructures. In some implementations, the light emitting diode furthercomprises an upper insulation layer covering at least part of thecurrent spreading layer, the upper insulation layer is disposed to formopenings exposing at least portions of the reflective electrodestructures, and the second electrode pad is placed over the upperinsulation layer and electrically connected to the exposed portions ofthe reflective electrode structures.

In another aspect, a light emitting diode module is provided to includea printed circuit board; and the light emitting diode bonded to theprinted circuit board, wherein the light emitting diode includes: afirst conductive-type semiconductor layer; a plurality of mesas placedon the first conductive-type semiconductor layer and each including anactive layer and a second conductive-type semiconductor layer;reflective electrode structures respectively placed on the mesas; ananti-diffusion reinforcing layer placed on each of the reflectiveelectrode structures; a first electrode pad electrically connected tothe first conductive-type semiconductor layer; and a second electrodepad electrically connected to the anti-diffusion reinforcing layer,wherein the first electrode pad and the second electrode pad arerespectively bonded to corresponding pads on the printed circuit boardvia solder paste.

In some implementations, the light emitting diode may further include acurrent spreading layer covering the plurality of mesas and the firstconductive-type semiconductor layer, including openings respectivelyplaced in upper regions of the mesas and exposing the reflectiveelectrode structures, forming ohmic contact with the firstconductive-type semiconductor layer, and insulated from the plurality ofmesas. The first electrode pad is electrically connected to the currentspreading layer.

In some implementations, the anti-diffusion reinforcing layer may beformed of the same material as that of the current spreading layer.Accordingly, the anti-diffusion reinforcing layer may be formed togetherwith the current spreading layer through the same process.

In some implementations, the current spreading layer may include Cr, Al,Ni, Ti, or Au.

In some implementations, the solder pastes may include Sn—Ag—Cu alloys.

In some implementations, the solder paste may comprise 50 wt % or moreof Sn of the total weight of metals.

In some implementations, the solder paste covers upper surfaces and atleast a portion of side surfaces of the first electrode pad and thesecond electrode pad. In some implementations, the solder paste is incontact with a surface of the light emitting diode that is locatedcloser to the first electrode pad and the second electrode pad than theother surface of the light emitting diode.

In another aspect, a light emitting diode is provided to comprise: afirst conductive-type semiconductor layer; a plurality of mesas placedover the first conductive-type semiconductor layer, each including anactive layer and a second conductive-type semiconductor layer; a firstelectrode pad electrically connected to the first conductive-typesemiconductor layer; and a second electrode pad electrically connectedto the second conductive-type semiconductor layer of each of the mesas,wherein each of the first electrode pad and the second electrode padcomprises a solder barrier layer and an oxidation barrier layer.

In some implementations, solder barrier layer includes Cr, Ti, Ni, Mo,TiW or W or a combination of Cr, Ti, Ni, Mo, TiW or W, and the oxidationbarrier layer includes an Au, Ag or organic material layer. In someimplementations, the light emitting diode module further comprises: asubstrate; a wavelength converter covering one surface of the substrate,wherein the first conductive-type semiconductor layer is formed over theother surface of the substrate.

In one aspect, a light emitting diode is provided to comprise: a firstconductive-type semiconductor layer; a plurality of mesas placed overthe first conductive-type semiconductor layer, each including an activelayer and a second conductive-type semiconductor layer; reflectiveelectrode structures placed over the mesas; an anti-diffusionreinforcing layer placed over each of the reflective electrodestructures; a first electrode pad electrically connected to the firstconductive-type semiconductor layer; and a second electrode padelectrically connected to the anti-diffusion reinforcing layer.

In some implementations, at least one of the plurality of mesas extendsin a direction to adjoin to an edge of the first conductive-typesemiconductor layer. In some implementations, the light emitting diodemodule further comprises: a current spreading layer formed over theplurality of mesas and the first conductive-type semiconductor layer andspaced apart from the anti-diffusion layer.

In another aspect, a method of fabricating a light emitting diodeincludes: forming a first conductive-type semiconductor layer, an activelayer and a second conductive-type semiconductor layer on a substrate;forming a plurality of mesas on the first conductive-type semiconductorlayer by patterning the second conductive-type semiconductor layer andthe active layer; forming reflective electrode structures on theplurality of mesas to form ohmic contact with the plurality of mesas,respectively; forming a current spreading layer that covers theplurality of mesas and the first conductive-type semiconductor layer,includes openings respectively placed in upper regions of the mesas andexposing the reflective electrode structures, forms ohmic contact withthe first conductive-type semiconductor layer and is insulated from theplurality of mesas; and forming a first electrode pad electricallyconnected to the current spreading layer and a second electrode padelectrically connected to the reflective electrode structures, whereineach of the first electrode pad and the second electrode pad may includea solder barrier layer and an oxidation barrier layer.

In some implementations, the method may further include forming ananti-diffusion reinforcing layer on the reflective electrode structure,wherein the anti-diffusion reinforcing layer may be formed together withthe current spreading layer, and the second electrode pad may beconnected to the anti-diffusion reinforcing layer.

In some implementations, The method may further include, before formingthe current spreading layer, forming a lower insulation layer thatcovers the plurality of mesas and the first conductive-typesemiconductor layer, and includes openings exposing the firstconductive-type semiconductor layer and openings respectively placed inupper regions of the mesas and exposing the reflective electrodestructures.

In some implementations, the method may further include forming an upperinsulation layer on the current spreading layer, the upper insulationlayer including openings exposing the reflective electrode structuresand may cover sidewalls of the openings of the current spreading layer.

In some implementations, the lower insulation layer may include asilicon oxide layer and the upper insulation layer may include a siliconnitride layer.

In some implementations, the method further comprise: before the formingof the plurality of mesas, forming the reflective electrode structuresover the second conductive-type semiconductor layer.

After the first electrode pad and the second electrode pad are formed,the substrate may be partially removed to become thin through grindingand/or lapping. Thereafter, the substrate is divided to provideindividual LED chips isolated from each other. Next, a wavelengthconverter may be coated onto the LED chips, and the LED chip having thewavelength converter is mounted on a printed circuit board via solderpaste, thereby providing an LED module.

The wavelength converter may be formed by coating a phosphor-containingresin onto the LED chip, followed by curing, or may be formed byspraying phosphor powder onto the LED chip via an aerosol sprayer.

Embodiments of the disclosed technology provide a light emitting diodecapable of preventing diffusion of metal elements of solder paste, andan LED module including the same. In addition, embodiments of thedisclosed technology provide a light emitting diode having improvedcurrent spreading performance, for example, a flip-chip type lightemitting diode. Further, embodiments of the disclosed technology providea light emitting diode that has improved reflectivity using a currentspreading layer and thus has improved light extraction efficiency.Furthermore, the light emitting diode according to the embodiments ofthe disclosed technology has a simple mesa structure, thereby enablingsimplification of an LED fabrication process. On the other hand, solderpaste may cover upper surfaces of electrode pads of a flip-chip typelight emitting diode while covering at least part of side surfacesthereof. Furthermore, the solder paste may contact a lower surface ofthe light emitting diode adjacent the electrode pads, whereby heatgenerated in the light emitting diode can be discharged through thesolder pastes. Further, the solder paste may cover at least part of theside surface of the light emitting diode to reflect light emittedthrough the side surface of the light emitting diode, thereby improvingluminous efficacy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side sectional view of a light emitting diodemodule according to one embodiment of the disclosed technology.

FIG. 2 to FIG. 11 are views illustrating a method of fabricating a lightemitting diode according to one embodiment of the disclosed technology,in which (a) is a plan view and (b) is a sectional view taken along lineA-A in each of FIG. 2 to FIG. 10.

FIG. 12 to FIG. 14 are views illustrating a method of fabricating alight emitting diode according to another embodiment of the disclosedtechnology, in which (a) is a plan view and (b) is a sectional viewtaken along line A-A.

FIG. 15 to FIG. 18 are views illustrating a method of fabricating alight emitting diode according to another embodiment of the disclosedtechnology, in which (a) is a plan view and (b) is a sectional viewtaken along line A-A.

FIG. 19 is a scanning electron microscopy (SEM) sectional view of an LEDmodule fabricated by a method according to one embodiment of thedisclosed technology.

DETAILED DESCRIPTION

A flip chip type light emitting diode is used to prevent light loss bythe P-electrode pad while improving heat dissipation efficiency, and avariety of electrode structures have been suggested to help currentspreading in a large flip chip type light emitting diode (for example,U.S. Pat. No. 6,486,499). For example, a reflective electrode is formedon the P-type semiconductor layer, and extensions for current spreadingare formed on an exposed region of the N-type semiconductor layer formedby etching the P-type semiconductor layer and the active layer.

The reflective electrode formed on the P-type semiconductor layerreflects light generated in the active layer to improve light extractionefficiency while facilitating current spreading in the P-typesemiconductor layer. On the other hand, the extensions connected to theN-type semiconductor layer help current spreading in the N-typesemiconductor layer to allow uniform generation of light over a wideactive area.

A light emitting diode having a large area of about 1 mm2 or more usedfor high power requires current spreading not only in the P-typesemiconductor layer but also in the N-type semiconductor layer. However,a conventional technique employs linear extensions having highresistance and thus has a limit in current spreading. Moreover, sincethe reflective electrode is restrictively placed on the P-typesemiconductor layer, a significant amount of light is absorbed into thepads and the extensions instead of being reflected by the reflectiveelectrode, thereby causing significant light loss.

In a final product, the light emitting diode is provided in the form ofan LED module. In general, the LED module includes a printed circuitboard and an LED package mounted on the printed circuit board, in whichthe light emitting diode is mounted in chip form within the LED package.A conventional LED chip is mounted on a sub-mount, a lead frame or alead electrode via silver paste or AuSn solder and packaged to form anLED package, which in turn is mounted on a printed circuit board or thelike via the solder paste. Accordingly, the pads on the LED chip areplaced apart from the solder paste, and bonded by a relatively stablebonding material such as silver paste or AuSn solder.

Recently, studies have been made to develop a technology for fabricatingan LED module by directly bonding pads of a light emitting diode to aprinted circuit board via solder paste. For example, an LED module isfabricated by directly mounting an LED chip on a PCB instead ofpackaging the LED chip, or by fabricating a so-called wafer level LEDpackage, followed by mounting the LED package on a printed circuitboard. Since the pads directly adjoin the solder paste in these LEDmodules, metal elements such as tin (Sn) in the solder paste diffuseinto the light emitting diode through the pads and can generate shortcircuit in the light emitting diode, thereby causing device failure.

Hereinafter, various implementations of the disclosed technology will bedescribed in more detail with reference to the accompanying drawings. Itshould be understood that the following embodiments are given by way ofillustration only to facilitate the understanding of someimplementations of the disclosed technology. Therefore, the disclosedtechnology is not limited to the following embodiments and may beembodied in different ways. Further, the widths, lengths, andthicknesses of certain elements, layers or features may be exaggeratedfor clarity, and like components will be denoted by like referencenumerals throughout the accompanying drawings.

FIG. 1 is a schematic side sectional view of a light emitting diodemodule according to one embodiment of the disclosed technology.

Referring to FIG. 1, an LED module includes a printed circuit board 51having pads 53 a and 53 b and an light emitting diode 100 bonded to theprinted circuit board 51 via solder pastes 55. The light emitting diode100 includes a first conductive-type semiconductor layer 23, a mesa M, afirst electrode pad 43 a, and a second electrode pad 43 b. In someimplementations, the light emitting diode 100 may include an upperinsulation layer 41 on a lower surface thereof. The mesa M includes anactive layer (not shown) and a second conductive-type semiconductorlayer (not shown). In some implementations, the light emitting diode mayinclude a substrate 21 and a wavelength converter 45.

The printed circuit board is or includes a substrate having a printedcircuit formed thereon and may include any substrate capable ofproviding an LED module.

In the related art, an LED chip is mounted on a printed circuit boardhaving a lead frame or lead electrodes thereon, and packaged to providean LED package, which in turn is mounted on a printed circuit board. Inthis embodiment, the first and second electrode pads 43 a and 43 bformed on the LED chip are directly mounted on the printed circuit board51 via the solder pastes.

On the printed circuit board, the light emitting diode is placed upsidedown in a flip-chip structure, and a surface of the substrate 21, forexample, a surface of the substrate opposite to the mesa M, is coveredwith the wavelength converter 45. The wavelength converter 45 may covernot only the lower surface of the substrate 21 but also a side surfaceof the substrate 21. Here, the substrate 21 may be or include a growthsubstrate for growing GaN-based semiconductor layers, for example, apatterned sapphire substrate (PSS). Further, a plurality of mesas M maybe placed on the first conductive-type semiconductor layer 23 so as tobe separated from each other.

The solder pastes 55 serve to bond the first electrode pad 43 a and thesecond electrode pad 43 b to the pads 53 a and 53 b on the printedcircuit board. The solder pastes 55 may cover lower surfaces of thefirst electrode pad 43 a and the second electrode pad 43 b, and maycover at least part of side surfaces of the first and second electrodepads 43 a and 43 b, as shown in FIG. 1. Further, the solder pastes 55may contact the upper insulation layer 41 placed on the lower surface ofthe light emitting diode 100. The solder pastes 55 directly contact thelower surface of the light emitting diode 100, thereby facilitating heatdissipation from the light emitting diode 100 through the solder pastes55. Furthermore, the solder pastes 55 may cover part of a side surfaceof the light emitting diode 100. The solder pastes 55 may cover part ofthe side surface of the substrate. With this structure, the lightemitting diode 100 can reflect light emitted from the side surfacethereof using the solder pastes 55, thereby improving efficiency oflight emitted from the light emitting diode 100.

For the description of the structure, the term “solder paste” may mean afinal bonding layer formed of or including a paste, which is or includesa mixture of metal powder, flux or an organic material. For thedescription of the method of fabricating an LED module, the term “solderpaste” may mean a paste, which is a mixture of metal powder, flux or anorganic material.

As a final bonding layer, the solder paste 55 contains Sn and othermetals. Sn may be present in an amount of 50 wt % or more of the totalweight of metals in the solder paste. In another embodiment, Sn ispresent in an amount of 60 wt % or more of the total weight of metals inthe solder paste. In a further embodiment, Sn is present in an amount of90 wt % or more of the total weight of metals in the solder paste.

The solder paste 55 may contain or include, for example, Sn/Pb, inamounts of 63 wt %/37 wt %, or may contain Sn/Pb/Ag in amounts of 62 wt%/36 wt %/2 wt %. The solder paste 55 may be a Pb-free alloy. Forexample, the solder paste 55 may contain Sn/Ag in amounts of 96.5 wt%/3.5 wt %. Further, the solder paste 55 may contain Sn/Ag/Cu in amountsof 96.5 wt %/3 wt %/0.5 wt %, 95.8 wt %/3.5 wt %/0.7 wt %, 95.5 wt %/3.8wt %/0.7 wt %, 95.5 wt %/3.9 wt %/0.6 wt %, or 95.5 wt %/4.0 wt %/0.5 wt%. In another embodiment, the solder paste 55 may contain Sn and Sb inamounts of 95 wt % and 5 wt %, respectively.

FIG. 1 schematically shows the LED module according to the embodimentfor convenience of description, and the structure and components of thelight emitting diode will become more apparent by the followingdescription of a method of fabricating a light emitting diode.

FIG. 2 to FIG. 11 are views illustrating a method of fabricating a lightemitting diode according to one embodiment of the disclosed technology,in which (a) is a plan view and (b) is a sectional view taken along lineA-A in each of FIG. 2 to FIG. 10.

Referring to FIG. 2, a first conductive-type semiconductor layer 23, anactive layer 25 and a second conductive-type semiconductor layer 27 aregrown on a substrate 21. The substrate 100 is or includes a substratecapable of growing GaN-based semiconductor layers, and may be, forexample, a sapphire substrate, a silicon carbide substrate, a galliumnitride (GaN) substrate, a spinel substrate, or the like. In someimplementations, the substrate may be a patterned substrate.

The first conductive-type semiconductor layer may include, for example,an n-type GaN-based layer, and the second conductive-type semiconductorlayer 27 may include, for example, a p-type GaN-based layer. Inaddition, the active layer 25 may include a single-quantum wellstructure or a multi-quantum well structure, and may include a welllayer and a barrier layer. The well layer may have compositionalelements selected depending upon a desired wavelength of light, and mayinclude, for example, InGaN.

A preliminary insulation layer 29 may be formed on the secondconductive-type semiconductor layer 27. The preliminary insulation layer29 may be formed of or include SiO₂ by, for example, chemical vapordeposition.

Then, a photoresist pattern 30 is formed. The photoresist pattern 30 hasopenings 30 a for forming reflective electrode structures. The openings30 a are formed such that a bottom of each opening has a smaller widththan an inlet of the openings 30 a. A negative type photoresistfacilitates formation of the photoresist pattern 30 having the openings30 a with such shape.

Referring to FIG. 3, the preliminary oxidation layer 29 is etched usingthe photoresist pattern 30 as an etching mask. The preliminary oxidationlayer 29 may be etched by wet etching. Accordingly, the preliminaryoxidation layer 29 in the openings 30 a of the photoresist pattern 30 isetched to form openings 29 a of the preliminary oxidation layer 29,which expose the second conductive-type semiconductor layer 27. Theopenings 29 a generally have a similar or greater area than a bottomarea of the openings 30 a of the photoresist pattern 30.

Referring to FIG. 4, reflective electrode structures 35 are formed usinglift-off technology. The reflective electrode structure 35 may include areflective metal section 31, a capping metal section 32, and anoxidation prevention metal section 33. The reflective metal section 31may include a reflective layer and a stress relief layer may be formedbetween the reflective metal section 31 and the capping metal section32. The stress relief layer relieves stress due to a difference incoefficient of thermal expansion between the reflective metal section 31and the capping metal section 32.

The reflective metal section 31 may be formed of or include, forexample, Ni/Ag/Ni/Au, and may have a total thickness of about 1600 Å. Asshown, the reflective metal section 31 may have an inclined sidesurface, that is, a structure in which a bottom surface has a greaterarea than an upper surface. Such a reflective metal section 31 may beformed by e-beam evaporation.

The capping metal section 32 covers the upper and side surface of thereflective metal section 31 to protect the reflective metal section 31.The capping metal section 32 may be formed by sputtering or by e-beamevaporation (for example, planetary e-beam evaporation) in which thesubstrate 21 is rotated in a tilted state during vacuum deposition. Thecapping metal section 32 may include Ni, Pt, Ti, or Cr, and may beformed by depositing, for example, about 5 pairs of Ni/Pt or about 5pairs of Ni/Ti. Alternatively, the capping metal section 32 may includeTiW, W, or Mo.

The stress relief layer may be formed of or include a material selectedin various ways depending upon the metallic materials of the reflectivelayer and the capping metal section 32. For example, when the reflectivelayer is composed of or includes Al or Al alloys and the capping metalsection 32 is composed of or includes W, TiW or Mo, the stress relieflayer may be a single layer including Ag, Cu, Ni, Pt, Ti, Rh, Pd or Cr,or a composite layer including Cu, Ni, Pt, Ti, Rh, Pd or Au. Further,when the reflective layer is composed of or includes Al or Al alloys andthe capping metal section 32 is composed of or includes Cr, Pt, Rh, Pdor Ni, the stress relief layer may be a single layer including Ag or Cu,or a composite layer including Ni, Au, Cu or Ag.

Further, when the reflective layer is composed of or includes Ag or Agalloys and the capping metal section 32 is composed of or includes W,TiW or Mo, the stress relief layer may be a single layer including Cu,Ni, Pt, Ti, Rh, Pd or Cr, or a composite layer including Cu, Ni, Pt, Ti,Rh, Pd, Cr or Au. Further, when the reflective layer is composed of orincludes Ag or Ag alloys and the capping metal section 32 is composed ofor includes Cr or Ni, the stress relief layer may be a single layerincluding Cu, Cr, Rh, Pd, TiW or Ti, or a composite layer including Ni,Au or Cu.

Further, the oxidation prevention metal section 33 includes Au in orderto prevent oxidation of the capping metal section 32, and may be formedof or include, for example, Au/Ni or Au/Ti. Ti exhibits good adhesion toan oxide layer such as SiO₂ and thus is preferred. The oxidationprevention metal section 33 may be formed by sputtering or by e-beamevaporation (for example, planetary e-beam evaporation) in which thesubstrate 21 is rotated in a tilted state during vacuum deposition.

After deposition of the reflective metal structures 35, the photoresistpattern 30 is removed and thus the reflective metal structures 35 remainon the second conductive-type semiconductor layer 27, as shown in FIG.4.

Referring to FIG. 5, a plurality of mesas M separated from each otherare formed on the first conductive-type semiconductor layer 21. Each ofthe plurality of mesas M includes the active layer 25 and the secondconductive-type semiconductor layer 27. The active layer 25 is placedbetween the first conductive-type semiconductor layer 23 and the secondconductive-type semiconductor layer 27. On the other hand, thereflective electrode structure 35 is placed on each of the mesas M.

The plural mesas M may be formed by patterning the secondconductive-type semiconductor layer 27 and the active layer 25 so as toexpose the first conductive-type semiconductor layer 23. The pluralmesas M may be formed to have inclined side surfaces using photoresistreflow technology. The inclined profile of the side surface of the mesaM improves extraction efficiency of light generated in the active layer25.

As shown, the plural mesas M may have an elongated shape and be formedparallel to each other. Such a shape simplifies formation of the pluralmesas M having the same shape in a plurality of chip areas on thesubstrate 21.

The reflective electrode structures 35 cover most region of an uppersurface of the mesa M and have substantially the same shape as the shapeof the mesas M in a plan view.

In the course of etching the second conductive-type semiconductor layer27 and the active layer 25, the preliminary oxidation layer 29 remainingthereon is also partially etched and removed. On the other hand, on eachof the mesas M, although the preliminary oxidation layer 29 may remainnear an edge of the reflective electrode structure 35, the preliminaryoxidation layer 29 may be removed by wet etching or the like.Alternatively, the preliminary oxidation layer 29 may be removed beforeformation of the mesas M.

Referring to FIG. 6, after formation of the plural mesas M, the firstconductive-type semiconductor layer 23 may be subjected to etching so asto divide LED areas in chip unit. Accordingly, the upper surface of thesubstrate 21 is exposed near the edge of the first conductive-typesemiconductor layer 23.

As shown in FIG. 6, the plurality of mesas M may be placed inside anupper region of the first conductive-type semiconductor layer 23. Insome implementations, the plurality of mesas M may be placed in islandshapes on the upper region of the first conductive-type semiconductorlayer 23. Alternatively, the mesas M may extend in one direction toreach an edge of an upper surface of the first conductive-typesemiconductor layer 23. For example, edges of lower surfaces of theplurality of mesas M in the one direction may coincide with the edge ofthe first conductive-type semiconductor layer 23 in the one direction.

Referring to FIG. 7, a lower insulation layer 37 is formed to cover theplurality of mesas M and the first conductive-type semiconductor layer23. The lower insulation layer 37 includes openings 37 a and 37 b toallow electrical connection to the first conductive-type semiconductorlayer 23 and the second conductive-type semiconductor layer 27. Forexample, the lower insulation layer 37 may include openings 37 b whichexpose the first conductive-type semiconductor layer 23 and openings 37a which expose the reflective electrode structures 35.

The openings 37 a are placed in upper regions of the mesas M to bebiased towards the same end of the mesas. On the other hand, theopenings 37 b may be placed in a region between the mesas M and near theedge of the substrate 21, and may have an elongated shape extendingalong the mesa M.

The lower insulation layer 37 may be formed of or include oxides such asSiO₂, nitrides such as SiNx, or insulation materials such as MgF₂ bychemical vapor deposition (CVD) or the like. The lower insulation layer37 may be formed to a thickness of, for example, 4000 Å to 12000 Å. Thelower insulation layer 37 may be composed of or include a single layeror multiple layers. In addition, the lower insulation layer 37 may beformed as a distributed Bragg reflector (DBR) in which low refractivematerial layers and high refractive material layers are alternatelystacked one above another. For example, an insulation reflective layerhaving high reflectivity may be formed by stacking, for example,SiO₂/TiO₂ layers or SiO₂/Nb₂O₅ layers.

Referring to FIG. 8, a current spreading layer 39 is formed on the lowerinsulation layer 37. The current spreading layer 39 covers the pluralityof mesas M and the first conductive-type semiconductor layer 23. Inaddition, the current spreading layer 39 includes openings 39 a, whichare placed in the upper regions of the mesas M and expose the reflectiveelectrode structures 35. The current spreading layer 39 may form ohmiccontact with the first conductive-type semiconductor layer 23 throughthe openings 37 b of the lower insulation layer 37. The currentspreading layer 39 is insulated from the plurality of mesas M and thereflective electrode structures 35 by the lower insulation layer 37.

Each of the openings 39 a of the current spreading layer 39 has agreater area than the openings 37 a of the lower insulation layer 37 toprevent the current spreading layer 39 from being connected to thereflective electrode structures 35. Thus, the openings 39 a havesidewalls placed on the lower insulation layer 37.

The current spreading layer 39 is formed substantially over the entiretyof the upper surface of the substrate excluding the openings 39 a.Accordingly, current can easily spread through the current spreadinglayer 39. The current spreading layer 39 may include a highly reflectivemetal layer such as an Al layer, and the highly reflective metal layermay be formed on a bonding layer such as a Ti, Cr or Ni layer. Inaddition, a protective layer having a single layer or composite layerstructure of Ni, Cr, or Au, and the like may be formed on the highlyreflective metal layer. The current spreading layer 39 may have amultilayer structure of, for example, Cr/Al/Ni/Ti/Ni/Ti/Au/Ti.

Referring to FIG. 9, an upper insulation layer 41 is formed on thecurrent spreading layer 39. The upper insulation layer 41 includes anopening 41 a which exposes the current spreading layer 39, and openings41 b which expose the reflective electrode structures 35. The opening 41a may have an elongated shape in a perpendicular direction with respectto the longitudinal direction of the mesa M, and have a greater areathan the openings 41 b. The openings 41 b expose the reflectiveelectrode structures 35, which are exposed through the openings 39 a ofthe current spreading layer 39 and the openings 37 a of the lowerinsulation layer 37. The openings 41 b have a smaller area than theopenings 39 a of the current spreading layer 39 and a greater area thanthe openings 37 a of the lower insulation layer 37. Accordingly,sidewalls of the openings 39 a of the current spreading layer 39 may becovered by the upper insulation layer 41.

The upper insulation layer 41 may be formed of or include siliconnitride to prevent diffusion of metal elements from the solder paste,and may have a thickness of 1 μm to 2 μm. When the upper insulationlayer 41 has a thickness of less than 1 μm, it is difficult to preventdiffusion of the metal elements of the solder paste.

Referring to FIG. 10, a first electrode pad 43 a and a second electrodepad 43 b are formed on the upper insulation layer 41. The firstelectrode pad 43 a is connected to the current spreading layer 39through the opening 41 a of the upper insulation layer 41 and the secondelectrode pad 43 b is connected to the reflective electrode structures35 through the openings 41 b of the upper insulation layer 41. The firstelectrode pad 43 a and the second electrode pad 43 b are used whenmounting the light emitting diode on the printed circuit board via thesolder pastes. Accordingly, in order to prevent short circuit of thefirst electrode pad 43 a and the second electrode pad 43 b by the solderpastes, a distance D between the electrode pads is preferably about 300μm or more.

The first and second electrode pads 43 a and 43 b may be formed at thesame time by the same process, for example, photolithography and etchingtechnology or lift-off technology. Each of the first and secondelectrode pads 43 a and 43 b may include a solder barrier layer and anoxidation barrier layer. The solder barrier layer prevents diffusion ofmetal elements of the solder paste and the oxidation barrier layerprevents oxidation of the solder barrier layer. The solder barrier layermay include Cr, Ti, Ni, Mo, TiW or W, and the oxidation barrier layermay include Au, Ag or an organic material.

For example, the solder barrier layer may include five pairs of Ti/Nilayers or five pairs of Ti/Cr layers, and the oxidation barrier layermay include Au. With this structure, it is possible to prevent diffusionof metal elements of the solder paste while reducing a total thicknessof the first and second electrode pads 43 a and 43 b to less than 2 μm,or less than 1 μm.

Thereafter, a lower surface of the substrate 21 is partially removed bygrinding and/or lapping to reduce the thickness of the substrate 21.Next, the substrate 21 is divided into individual chip units, therebyproviding separate light emitting diodes. The substrate 21 may beremoved from the LED chips before or after division into the individualLED chip units.

Referring to FIG. 11, a wavelength converter 45 is formed on each of theseparate light emitting diodes. The wavelength converter 45 may beformed by coating a phosphor-containing resin onto the light emittingdiode using a printing technique, or may be formed by spraying phosphorpowder onto the substrate 21 using an aerosol sprayer. For example,aerosol deposition can form a uniform phosphor film on the lightemitting diode, thereby improving color uniformity of light emitted fromthe light emitting diode. Accordingly, after completion of the lightemitting diode according to the embodiments of the disclosed technology,the light emitting diode is bonded to the corresponding pads 55 of theprinted circuit board 51 via the solder pastes as shown in FIG. 1,thereby providing a final LED module.

FIG. 12 to FIG. 14 are views illustrating a method of fabricating alight emitting diode according to another embodiment of the disclosedtechnology, in which (a) is a plan view and (b) is a sectional viewtaken along line A-A.

Referring to FIG. 12, the LED fabrication method according to thisembodiment is generally similar to the LED fabrication method accordingto the embodiment described with reference to FIG. 2 to FIG. 11 exceptfor formation of an anti-diffusion reinforcing layer 40.

In the LED fabrication method according to this embodiment, a lowerinsulation layer 37 is formed through the process as described withreference to FIG. 2 to FIG. 7. Then, as described with reference to FIG.8, a current spreading layer 39 is formed. Here, during formation of thecurrent spreading layer 39, an anti-diffusion reinforcing layer 40 isformed on reflective electrode structures 35. The anti-diffusionreinforcing layer 40 may be formed of or include the same material bythe same process as those of the current spreading layer 39 and may bespaced from the current spreading layer 39.

Referring to FIG. 13, an upper insulation layer 41 is formed asdescribed with reference to FIG. 9. Here, openings 41 b of the upperinsulation layer 41 expose the anti-diffusion reinforcing layer 40.

Referring to FIG. 14, first and second electrode pads 43 a and 43 b areformed as described with reference to FIG. 10. The second electrode pad43 b is connected to the anti-diffusion reinforcing layer 40. Thus, theanti-diffusion reinforcing layer 40 is placed between the reflectivemetal structure 35 and the second electrode pad 43 b and preventsdiffusion of metal elements of the solder paste to the reflective metalstructure 35.

Then, the substrate is divided into individual LED chip units and thewavelength converter 45 is formed as described with reference to FIG.11.

FIG. 15 to FIG. 17 are views illustrating a method of fabricating alight emitting diode according to another embodiment of the disclosedtechnology, in which (a) is a plan view and (b) is a sectional viewtaken along line A-A.

In the above embodiments, the mesas M are formed after formation of thereflective electrode structure 35. On the contrary, in this embodiment,the mesas M are formed before formation of the reflective electrodestructure 35.

Referring to FIG. 15, a first conductive-type semiconductor layer 23, anactive layer 25 and a second conductive-type semiconductor layer 27 aregrown on a substrate 21, as described with reference to FIG. 2. Then, aplurality of mesas M is formed through a patterning process. The mesas Mare similar to those described with reference to FIG. 5 and thus adetailed description thereof is omitted herein.

Referring to FIG. 16, a preliminary oxidation layer 29 is formed tocover the first conductive-type semiconductor layer 23 and the pluralityof mesas M. The preliminary oxidation layer 29 may be formed of orinclude the same material by the same process as described withreference to FIG. 2. A photoresist pattern 30 having openings 30 a isformed on the preliminary oxidation layer 29. The openings 30 a of thephotoresist pattern 30 are placed within upper regions of the mesas M.The photoresist pattern 30 is the same as the photoresist patterndescribed with reference to FIG. 1 except that the photoresist pattern30 is formed on the substrate having the mesas M formed thereon, andthus a detailed description thereof is omitted herein.

Referring to FIG. 17, the preliminary oxidation layer 29 is etched usingthe photoresist pattern 30 as an etching mask, whereby openings 29 aexposing the second conductive-type semiconductor layer 27 are formed.

Thereafter, referring to FIG. 18, reflective electrode structures 35 areformed on the mesas M by a lift-off technique, as described in detailwith reference to FIG. 4. Then, light emitting diodes can be fabricatedthrough processes similar to those described with reference to FIG. 6 toFIG. 11.

In this embodiment, since the mesas M are formed prior to the reflectiveelectrode structures 35, the preliminary oxidation layer 29 can remainon side surfaces of the mesas M and on a region between the mesas M.Then, the preliminary oxidation layer 29 is covered with the lowerinsulation layer 39 and is subjected to patterning together with thelower insulation layer 39.

As in this embodiment, the sequence of the processes in fabrication ofthe light emitting diode can be modified in various ways. For example, aprocess of isolating LED regions (ISO process) may be performed beforeformation of the mesas M or before formation of the reflective electrodestructures 35.

FIG. 19 is a scanning electronic microscopy (SEM) sectional view of anLED module fabricated by a method according to one embodiment of thedisclosed technology. Here, (b) shows an SEM sectional view of a solderpaste at one side of the SEM section view of (a).

Referring to FIGS. 19 (a) and (b), an light emitting diode 100 is bondedto a printed circuit board 51 having pads 53 via solder pastes 55. Thesolder pastes 55 bond electrode pads 43 to the pads 53 on the printedcircuit board 51. In addition, the solder pastes 55 are placed not onlybetween the electrode pads 43 and the pads 53, but also on part of sidesurfaces of the electrode pads 43, and also contact the upper insulationlayer 41. In addition, as shown in the figure, some of the solder pastes55 covers a portion of a side surface of the light emitting diode 100.

What is claimed is:
 1. A light emitting diode comprising: a firstconductive-type semiconductor layer; a mesa placed on the firstconductive-type semiconductor layer, the mesa including an active layerand a second conductive-type semiconductor layer; a reflective electrodestructure placed on the mess; a current spreading layer covering themesa and the first conductive-type semiconductor layer, and including anopening placed in an upper region of the mesa while exposing thereflective electrode structure, the current spreading layer formingohmic contact with the first conductive-type semiconductor layer andbeing insulated from the mesa; a lower insulation layer placed betweenthe mesa and the current spreading layer and insulating the currentspreading layer from the mesa, the lower insulation layer including anopening placed in the upper region of the mesa and exposing thereflective electrode structure; an upper insulation layer covering atleast part of the current spreading layer and including an opening onthe reflective electrode structure, wherein the opening of the upperinsulation layer is narrower than the opening of the lower insulationlayer.
 2. The light emitting diode of claim 1, wherein the upperinsulation layer covers a sidewall of the opening of the lowerinsulation layer.
 3. The light emitting diode of claim 1, wherein theopening of the upper insulation layer is narrower than the opening ofthe current spreading layer.
 4. The light emitting diode of claim 3,wherein the upper insulation layer covers a sidewall of the opening ofthe current spreading layer.
 5. The light emitting diode of claim 1,wherein the upper insulation layer covers sidewalls of the openings ofthe current spreading layer and the lower insulation layer.
 6. The lightemitting diode of claim 1, wherein the opening of the current spreadinglayer has a greater width than the opening of the lower insulation layerto expose the opening of the lower insulation layer.
 7. The lightemitting diode of claim 1, wherein the opening of the upper insulationlayer exposes the reflective electrode structure.
 8. The light emittingdiode of claim 1, further comprising: an anti-diffusion reinforcinglayer placed on the reflective electrode structure and in the opening ofthe current spreading layer, wherein the opening of the upper insulationlayer exposes the anti-diffusion reinforcing layer.
 9. The lightemitting diode of claim 8, wherein the anti-diffusion reinforcing layeris formed of the same material as that of the current spreading layer.10. The light emitting diode of claim 8, wherein the opening of theupper insulation layer is limitedly placed on the anti-diffusionreinforcing layer.
 11. The light emitting diode of claim 1, wherein thereflective electrode structure comprises a reflective metal section, acapping metal section, and an oxidation prevention metal section, thereflective metal section having an inclined side surface such that anupper surface of the reflective metal section has a narrower area than alower surface thereof, the capping metal section covering the upper andside surfaces of the reflective metal section, a stress relief layerbeing formed at an interface between the reflective metal section andthe capping metal section.
 12. The light emitting diode of claim 1,further comprising: a first electrode pad electrically connected to thefirst conductive-type semiconductor layer; and a second electrode padelectrically connected to the second conductive-type semiconductorlayer, wherein the first electrode pad and the second electrode pad aredisposed on the upper insulation layer, and the second electrode pad isoverlapped to the openings of the lower insulation layer, the currentspreading layer and the upper insulation layer.
 13. The light emittingdiode of claim 12, wherein each of the first electrode pad and thesecond electrode pad comprises a solder barrier layer and an oxidationbarrier layer.
 14. The light emitting diode of claim 13, wherein thesolder barrier layer comprises a metal layer including Cr, Ti, Ni, Mo,TiW or W or a combination of any two of Cr, Ti, Ni, Mo, TiW or W, andthe oxidation barrier layer comprises an Au, Ag or organic materiallayer.
 15. The light emitting diode of claim 12, wherein the firstelectrode pad is connected to the current spreading layer and the secondelectrode pad is connected to the reflective electrode structure. 16.The light emitting diode of claim 12, further comprising: ananti-diffusion reinforcing layer placed on the reflective electrodestructure and in the opening of the current spreading layer, wherein thefirst electrode pad is connected to the current spreading layer, and thesecond electrode pad is connected to the anti-diffusion reinforcinglayer.
 17. The light emitting diode of claim 1, wherein the opening ofthe current spreading layer is placed to be biased towards an edge ofthe mesa.
 18. The light emitting diode of claim 1, wherein the currentspreading layer comprises a reflective metal.
 19. The light emittingdiode of claim 1, wherein the lower insulation layer comprises a siliconoxide layer and the upper insulation layer comprises a silicon nitridelayer.
 20. The light emitting diode of claim 1, further comprising: asubstrate; and a wavelength converter covering an upper surface of thesubstrate.